Porous membranes for high pressure filtration

ABSTRACT

The present invention relates to a porous membrane suitable for use in high pressure filtration method.

CROSS-RELATED REFERENCE

This application claims priority to European patent application No. 18214572.2 filed on Dec. 20, 2018, the whole content of this application being incorporated herein by reference for all purposes.

TECHNICAL FIELD

The present invention relates to a porous membrane suitable for use in high pressure filtration method.

BACKGROUND ART

Porous membranes are discrete, thin interface that moderate the permeation of chemical species in contact with them. The key property of porous membranes is their ability to control the permeation rate of chemical species through the membrane itself. This feature is exploited in many different applications like separation applications (water and gas) or drug delivery applications.

Aromatic polymers (such as polysulphones and polyethersulphone), partially fluorinated polymers (such as polyvinylidene fluoride) and polyamides are widely used in the preparation of microfiltration and ultrafiltration membranes due to their good mechanical strength and thermal stability.

Polymeric membranes suitable for use as microfiltration and ultrafiltration typically control the permeation under a “sieve” mechanism since the passage of liquid or gas is mainly governed by a convective flux. Such polymeric membranes are mainly produced by phase inversion methods which can give raise to items with very large fraction of voids (porosity).

A homogeneous polymeric solution (also referred to as “dope solution”) containing a polymer, a suitable solvent and/or a co-solvent and, optionally, one or more additives is typically processed by casting into a film and then brought to precipitation by contacting it with a non-solvent medium by the so-called Non-Solvent Induced Phase Separation (NIPS) process. The non-solvent medium is usually water or a mixture of water and surfactants, alcohols and/or the solvent itself.

Precipitation can also be obtained by decreasing the temperature of the polymeric solution by the so-called Thermal Induced Phase Separation (TIPS) process.

Alternatively, the precipitation may be induced by contacting the film processed by casting with air at a very high water vapour content by the so-called Vapour Induced Phase Separation (VIPS) process.

Still, the precipitation may be induced by evaporation of the solvent from the film processed by casting by the so-called Evaporation Induced Phase Separation (EIPS) process. Typically in this process an organic solvent with low boiling point (such as THF, acetone, MEK and the like) is used in admixture with water (the so called “non-solvent”). The polymer solution is first extruded and then precipitates due to the evaporation of the volatile solvent and the enrichment of the non-solvent.

The above processes can be used in combination and/or in sequence to provide membranes having specific morphology and performances. For example, EIPS process can be combined with the VIPS process and NIPS process in order to complete the coagulation process.

The EIPS process is known as “thermal coagulation process” when polyurethane polymers are used to manufacture porous membranes. In this case, the dope solution is prepared with a pre-polymer and as the membrane is formed, it is stabilized with a thermal post treatment to fix the porous structure and crosslink the pre-polymer.

In addition, stretching (either during or after the coagulation process) under heating is a way known in the art to increase the porosity and the pore size.

The use of porous membranes, notably in the form of thin film composite (TFC), for the separation of liquid or gases in reverse osmosis or ultrafiltration processes is well known.

Reverse osmosis has attracted considerable interest in the field of purification of saline water. In this process, high pressure saline water may be placed in contact with a semipermeable membrane (typically made from a polyamide layer), which is permeable to water but relatively impermeable to salt. Concentrated brine and relatively pure water are separated thereby; the relatively pure water may then be utilized for personal use such as drinking, cooking, etc., while the brine may be discarded.

In addition, TFC membranes may also be utilized for the separation of various gases. The separation of a gas mixture utilizing a membrane is effected by passing a feed stream of the gas across the surface of the membrane. Since the feed stream is at an elevated pressure relative to the effluent stream, a more permeable component of the mixture will pass through the membrane at a more rapid rate than will a less permeable component. Therefore, the permeate stream which passes through the membrane is enriched in the more permeable component while, conversely, the residue stream is enriched in the less permeable component of the feed.

Efficiency of the reverse osmosis process depends to a large extent on the nature of the membrane and numerous types of membranes from several kind of polymers, and methods of preparing them have been described in the prior art, for example in U.S. Pat. No. 4,039,440 (U.S.A. DEPARTMENT OF THE INTERIOR), in U.S. Pat. No. 8,177,978 (NANOH20, INC.) and in U.S. Pat. No. 5,250,185 (TEXACO INC.).

However, the Applicant noted that membranes known in the art, when subjected to high operating pressures, tend to undergo compaction which then results in reduced permeate productivity after a period of time. The compaction of the membrane is due to the collapse of the relatively weak porous structure under pressure. Also, the unavoidable external surface fouling leads to increase the required feed pressure. The external fouling and the collapse of the porous structure inevitably contribute to modifying the membrane's macrovoid structure, by reducing the void volume and increasing the hydraulic resistance.

Reverse osmosis membranes may be fabricated including nanoparticles in the porous support membrane to release soluble metal ions for the interfacial polymerization process and/or improve flux flow decline by, perhaps, resisting compaction of the support membranes during reverse osmosis. Nanocomposite materials technology for the manufacture of reverse osmosis membrane were evaluated and discussed, for example, by PENDERGAST, Mary Theresa M., et al. Using nanocomposite materials technology to understand and control reverse osmosis membrane compaction. Desalination. 2010, vol. 261, p. 255-263.

However, the use of said nanoparticles is not desired because, on the one hand, they interfere with the phase-inversion process by modifying the viscosity of the dope solution and the coagulation process, such that after coagulation the membrane does not show a uniform distribution of particles. In addition, on the other hand, the risk of leaching exists, which provides for serious concerns from the regulatory point of view in terms of toxicological profile.

The possibility of manufacturing membranes and filters from compositions comprising aromatic polymers have been broadly disclosed in the art. For example, EP 1858977 B (SOLVAY ADVANCED POLYMERS LLC) broadly disclose a blend composition comprising polyphenylene and/or poly(aryl ether sulfone) for the preparation of articles, such as among the others membraned and filters.

The use of polymers comprising phenylene repeating units has been disclosed in the art for the manufacture of ion-exchange membranes, which are actually non-porous films. For example, U.S. Pat. No. 7,868,124 (COMMISSARIAT A L'ENERGIE ATOMIQUE) discloses polymers comprising phenylene units, at least one of which bears a phenylene side group substituted with a perfluoro group or chain, which itself bears a —SO₃H, —PO₃H₂ or —COOH group, and the use thereof to make fuel cell membranes. Also, U.S. Pat. No. 7,888,397 (SANDIA CORPORATION) discloses polyphenylene-based anion exchange membrane. U.S. Pat. No. 7,906,608 (JSR CORPORATION) discloses a nitrogen-containing aromatic compound, which enables to the manufacture of polymers endowed with proton conductivity. Said polymers can be used to manufacture proton-conductive films.

Q. Shi et al. in “Poly(p-phenylene terephthalamide) embedded in a polysulfone as the substrate for improving compaction resistance and adhesion of a thin film composite polyamide membrane” J. Mater. Chem. A, 2017, 5, 13610-13624 disclose an approach for improve the compaction resistance and polyamide skin layer adhesion onto the substrate in thin film composite (TFC) membranes, which is based on in situ polymerization of p-phenylene terephthamide (PPTA) in a polysulfone (PSf) solution prior to membrane casting via the phase inversion phase, thereby forming a PPTA-embedded PSf substrate. In brief, this article disclose a reaction for bonding PPTA to PSf, and not the physical blend of two components.

WO 2008/116837 (Solvay Advanced polymers, L.L.C.) discloses a fiber made with a polymer material selected from different aromatic polymers. preferred methods for the manufacture of the fibers are those wherein the starting polymer are in the melt state. Said fiber can be then incorporated into a fabric, such as for use in textile industry and aerospace, automotive, medical, military, safety, chemical, pharmaceutical and metallurgical industries. The fabric can be incorporated into a filter assembly, which can be used for industrial plants, such as electric power plants and cement plants. No example of the fibers or the fabrics as described above are provided in this patent application. Also, this patent application describes filters, not membranes, which are known to have different physical properties, notably in terms of pore size dimensions.

However, to the knowledge of the Applicant, the use of membranes made from polyphenylene polymers for high-pressure filtration has never been disclosed in the art.

SUMMARY OF INVENTION

The Applicant thus faced the problem of providing a membrane that does not undergo to compaction when used in high-pressure filtration methods.

The Applicant also faced the problem of providing a membrane having outstanding mechanical properties, such that a membrane having low thickness can be manufactured.

Also, the Applicant faced the problem of providing a membrane showing the above mentioned properties, without the use of mineral fillers or other additives in the starting dope compositions.

Surprisingly, the Applicant found that a membrane comprising at least one porous layer comprising at least one aromatic sulfone polymer and at least one polyphenylene polymer is suitable for use in high-pressure filtration methods.

The Applicant surprisingly found that the membrane according to the present invention is capable of resisting to high pressure, without showing compaction or flux decay.

Thus, in a first aspect, the present invention relates to a method for purifying a fluid containing at least one contaminant, said method comprising the steps of

(I) providing a fluid containing at least one contaminant; (II) providing a membrane [membrane (PSP)] comprising at least one porous layer [layer (PSP comprising at least one aromatic sulfone polymer [polymer (SP)] and at least one polyphenylene polymer [polymer (PP)]; (III) contacting said fluid containing at least one contaminant and said membrane (PSP) by applying a pressure higher than 1 bar to said fluid; and (IV) recovering the fluid free from said at least one contaminant.

Also, the Applicant found that membrane (PSP) according to the present invention has outstanding mechanical properties, even when a membrane with thickness of about 10 micron is manufactured.

Also, the Applicant found that membrane (PSP) according to the present invention has outstanding resistance to strong alkaline environment, and hence provides an advantage over membranes made from composition comprising fluorinated polymers such as polyvinylidenfluoride (PVDF), whose polymeric structure is altered until it breaks when used in strongly alkaline environments.

Advantageously, said membrane (PSP) is prepared from a composition [composition (C)] comprising at least one polymer (SP), at least one polymer (PP) and at least one solvent [medium (L)].

Advantageously, said polymer (PP) and said polymer (SP) are the only polymers in said composition (C).

Thus, in a further aspect, the present invention relates to a membrane [membrane (PSP*)] comprising at least one porous layer [layer (PSP*)] obtained from a composition [composition (C*)] comprising:

-   -   at least one sulfone polymer [polymer (SP)] in an amount of from         7 to 60 wt. % based on the total weight of said composition         (C*),     -   at least one polyphenylene polymer [polymer (PP)] in an amount         of from 0.1 to less than 30 wt. % based on the total weight of         said composition (C*), and     -   at least one solvent [medium (L)] in an amount of from 10 to         92.9 wt. % based on the weight of said composition (C*).

Indeed, the Applicant found that when a said composition (C*) comprises an amount of said polymer (SP) of less than 7 wt. % based on the total weight if said composition (C*), despite the addition of polymer (PP) as additive in composition (C*), the porous layer obtained is too fragile for subsequent manipulation, and hence the membrane obtained therefrom does not have sufficient mechanical strength to be handled by a technician and even less to withstand under high pressure.

Also, the Applicant found that when said composition (C*) comprises an amount of said polymer (PP) higher than 30 wt. % based on the weight of said composition (C*), the polymer (PP) does not dissolve in the medium (L) and hence it is not possible to manufacture a membrane.

DESCRIPTION OF EMBODIMENTS

For the purposes of the present description:

-   -   the use of parentheses before and after symbols or numbers         identifying compounds, chemical formulae or parts of formulae         has the mere purpose of better distinguishing those symbols or         numbers from the rest of the text and hence said parentheses can         also be omitted;     -   the term “membrane” is intended to indicate to a discrete,         generally thin, interface that moderates the permeation of         chemical species in contact with it, said membrane containing         pores of finite dimensions;     -   the term “gravimetric porosity” is intended to denote the         fraction of voids over the total volume of the porous membrane;     -   the term “solvent” is used herein in its usual meaning, that is         it indicates a substance capable of dissolving another substance         (solute) to form an uniformly dispersed mixture at the molecular         level. In the case of a polymeric solute, it is common practice         to refer to a solution of the polymer in a solvent when the         resulting mixture is transparent and no phase separation is         visible in the system. Phase separation is taken to be the         point, often referred to as “cloud point”, at which the solution         becomes turbid or cloudy due to the formation of polymer         aggregates.

Membranes containing pores homogeneously distributed throughout their thickness are generally known as symmetric (or isotropic) membranes; membranes containing pores which are heterogeneously distributed throughout their thickness are generally known as asymmetric (or anisotropic) membranes.

Said membrane (PSP) may be either a symmetric membrane or an asymmetric membrane.

The asymmetric porous membrane (PSP) typically comprises an outer layer containing pores having an average pore diameter smaller than the average pore diameter of the pores in one or more inner layers.

The membrane (PSP) preferably has an average pore diameter of at least 0.001 μm, more preferably of at least 0.005 μm, and even more preferably of at least 0.01 μm. The membrane (PSP) preferably has an average pore diameter of at most 50 μm, more preferably of at most 20 μm and even more preferably of at most 15 μm.

Suitable techniques for the determination of the average pore diameter in the porous membranes of the invention are described for instance in Handbook of Industrial Membrane Technology. Edited by PORTER, Mark C. Noyes Publications, 1990. p. 70-78. Average pore diameter is preferably determined by scanning electron microscopy (SEM).

The membrane (PSP) typically has a gravimetric porosity comprised between 5% and 90%, preferably between 10% and 85% by volume, more preferably between 30% and 90%, based on the total volume of the membrane.

Suitable techniques for the determination of the gravimetric porosity in membrane (PSP) are described for instance by SMOLDERS, K., et al. Terminology for membrane distillation. Desalination. 1989, vol. 72, p. 249-262.

Membrane (PSP) may be either a self-standing porous membrane comprising said layer (PP) as the only layer or a multi-layered membrane, preferably comprising said layer (PSP) supported onto a substrate.

Said substrate layer may be partially or fully interpenetrated by said layer (PSP).

A multi-layered membrane is typically obtained by coating said substrate with said layer (PSP) or by impregnating or dipping said substrate with said composition (C) as defined above.

The nature of the substrate is not particularly limited. The substrate generally consists of materials having a minimal influence on the selectivity of the porous membrane. The substrate layer preferably consists of non-woven materials, glass fibers and/or polymeric material such as for example polypropylene, polyethylene and polyethyleneterephthalate.

In addition to the substrate, membrane (PP) can comprise an additional layer, which is preferably a coating with aromatic polyamides.

Depending on its final intended use, membrane (PSP) can be flat, when flat membranes are required, or tubular in shape, when tubular or hollow fiber membranes are required.

Flat membranes are generally preferred when high fluxes are required whereas hollow fibers membranes are particularly advantageous in applications wherein compact modules having high surface areas are required.

Flat membranes preferably have a thickness comprised between 10 μm and 200 μm, more preferably between 15 μm and 150 μm.

Preferably, when membrane (PSP) of the invention is in the form of a flat membrane, it is characterized by a tensile modulus (measured according to ASTM D638 type V) of at least 235 MPa, more preferably of at least 250 MPa.

In addition, the Applicant found that in order to withstand a working pressure higher than 1 bar, membrane (PP*) according to the present invention must possess a combination of mechanical properties, in terms of ratio between the tensile modulus as defined above and gravimetric porosity (as defined above) higher than 310 MPa and preferably higher than 340 MPa.

Tubular membranes typically have an outer diameter greater than 3 mm. Tubular membranes having an outer diameter comprised between 0.5 mm and 3 mm are typically referred to as hollow fibers membranes. Tubular membranes having a diameter of less than 0.5 mm are typically referred to as capillary membranes.

For the purpose of the invention, the term “aromatic sulfone polymer [polymer (SP)]” is intended to denote any polymer comprising recurring units wherein more than 50% by moles of the recurring units of said polymer (SP) are connected by ether linkages in the main chain and comprise at least one group of formula —Ar—SO₂—Ar′— [recurring units (R_(SP))], wherein Ar and Ar′, equal to or different from each other, are aromatic groups.

In a first preferred embodiment of the invention, the recurring units (R_(SP)) of the polymer (SP) are preferably recurring units (R_(SP-1)) of formula:

—Ar¹-(T′-Ar²)_(n)—O—Ar³—SO₂—[Ar⁴-(T-Ar²)_(n)—SO₂]_(m)—Ar⁵—O—  (R_(SP-1))

wherein:

-   -   Ar¹, Ar², Ar³, Ar⁴, and Ar⁵, equal to or different from each         other and at each occurrence, are independently aromatic mono-         or polynuclear groups;     -   T and T′, equal to or different from each other and at each         occurrence, is independently a bond or a divalent group         optionally comprising one or more than one heteroatoms;         preferably T′ is selected from the group consisting of a bond,         —CH₂—, —C(O)—, —C(CH₃)₂—, —C(CF₃)₂—, —C(═CCl₂)—, —SO₂—,         —C(CH₃)(CH₂CH₂COOH)—, and a group of formula:

and preferably T is selected from the group consisting of a bond, —CH₂—, —C(O)—, —C(CH₃)₂—, —C(CF₃)₂—, —C(═CCl₂)—, —C(CH₃)(CH₂CH₂COOH)—, and a group of formula:

and

-   -   n and m, equal to or different from each other, are         independently zero or an integer of 1 to 5.

Non limiting examples of polymers (SP) according to this first preferred embodiment of the invention include poly(phenylene sulfone) polymers [polymers (PPSU)], poly(sulfone) polymers [polymers (PSU)] and poly(ether sulfone) polymers [polymers (PESU)].

For the purpose of the invention, the term “poly(phenylene sulfone) polymer [polymer (PPSU)]” is intended to denote any polymer comprising recurring units wherein more than 50% by moles of the recurring units (R_(SP-1)) of said polymer (PPSU) are recurring units (R_(PPSU)) of formula (K-A):

In a preferred embodiment of the present invention, more than 75% by moles, preferably more than 90% by moles, more preferably more than 99% by moles, even more preferably substantially all the recurring units (R_(SP-1)) of the polymer (PPSU) are recurring units (R_(PPSU)) of formula (K-A), chain defects or minor amounts of other recurring units might be present, being understood that these latter do not substantially modify the properties of the polymer (PPSU).

The polymer (PPSU) polymer may be notably a homopolymer or a copolymer such as a random copolymer or a block copolymer. When the (PPSU) polymer is a copolymer, its recurring units are advantageously a mix of recurring units (R_(PPSU)) of formula (K-A) and of recurring units (R_(PPSU*)), different from recurring units (R_(PPSU)), such as recurring units of formula (K-B), (K-C) or (K-D):

and mixtures thereof.

The polymer (PPSU) can also be a blend of a homopolymer and a copolymer as defined above.

Non-limiting examples of polymers (PPSU) suitable for the invention include those commercially available under the trademark names RADEL® R PPSU from Solvay Specialty Polymers USA L.L.C.

For the purpose of the present invention, the term “poly(sulfone) polymer [polymer (PSU)]” is intended to denote an aromatic sulfone polymer wherein at least 50% by moles, preferably at least 60% by moles, more preferably at least 70% by moles, even more preferably at least 80% by moles and most preferably at least 90% by moles of the recurring units (R_(SP-1)) of said polymer (PSU) are recurring units (R_(PSU)) of formula:

Non-limiting examples of polymers (PSU) suitable for the invention include those commercially available under the trademark name UDEL® PSU from Solvay Specialty Polymers USA L.L.C.

For the purpose of the present invention, the term “poly(ether sulfone) polymer [polymer (PESU)]” is intended to denote any polymer wherein more than 50% by moles of the recurring units (R_(SP-1)) of said polymer (PESU) are recurring units (R_(PESU)) of formula:

wherein each of R′, equal to or different from each other, is selected from the group consisting of halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium, and each of j′, equal to or different from each other and at each occurrence, is independently zero or is an integer from 0 to 4.

Preferred recurring units (R_(PESU)) are those complying with formula (I), shown below:

The polymer (PESU) may be notably a homopolymer or a copolymer such as a random or a block copolymer.

When the polymer (PESU) is a copolymer, its recurring units are advantageously a mix of recurring units (R_(PESU)), as defined above, and of recurring units (R_(PESU*)). The recurring units (R_(PESU*)) are typically selected from the group consisting of those of formulae (II), (III) and (IV) here below:

(II)

wherein:

-   -   each of R′, equal to or different from each other, is selected         from the group consisting of halogen, alkyl, alkenyl, alkynyl,         aryl, ether, thioether, carboxylic acid, ester, amide, imide,         alkali or alkaline earth metal sulfonate, alkyl sulfonate,         alkali or alkaline earth metal phosphonate, alkyl phosphonate,         amine and quaternary ammonium;     -   each of i′, equal to or different from each other and at each         occurrence, is independently zero or is an integer from 0 to 4;     -   each of T, equal to or different from each other, is selected         from the group consisting of a bond, —CH₂—; —O—; —S—; —C(O)—;         —C(CH₃)₂—; —C(CF₃)₂—; —C(═CCl₂)—; —C(CH₃)(CH₂CH₂COOH)—; —N═N—;         —R^(a)C═CR^(b)—; where each R^(a) and R^(b), independently of         one another, is a hydrogen or a C₁-C₁₂-alkyl, C₁-C₁₂-alkoxy, or         C₆-C₁₈-aryl group; —(CH₂)_(q)— and —(CF₂)_(q)— wherein q is and         integer from 1 to 6, or an aliphatic divalent group, linear or         branched, of up to 6 carbon atoms; and mixtures thereof.

Specific recurring units (R_(PESU*)) are typically selected from the group consisting of those of formula (A), (B) and (C) here below:

and mixtures thereof.

The polymer (PESU) may be a blend of the previously cited homopolymer and copolymer.

Preferably more than 75% by moles, preferably more than 85% by moles, preferably more than 95% by moles, preferably more than 99% by moles of the recurring units of the polymer (PESU) are recurring units (R_(PESU)), as defined above.

Most preferably, all the recurring units of the polymer (PESU) are recurring units (R_(PESU)), as defined above, chain defects, or very minor amounts of other units might be present, being understood that these latter do not substantially modify the properties.

Non-limiting examples of polymers (PESU) suitable for the invention include, for instance, those described in WO 2014/072447 (SOLVAY SPECIALTY POLYMERS ITALY S.P.A.) 15 May 2014.

Non-limiting examples of polymers (PESU) suitable for the invention include those commercially available under the trademark name VERADEL® PESU from Solvay Specialty Polymers USA L.L.C.

In a second preferred embodiment of the invention, the recurring units (R_(SP)) of the polymer (SP) are preferably recurring units (R_(SP-2)) of formula:

—Ar^(*1)—SO₂—[Ar^(*2)-(T*-Ar^(*3))_(n*)—SO₂]_(m*)—Ar^(*4)-E-  (R_(SP-2))

wherein

-   -   each of Ar^(*1), Ar^(*2), Ar^(*3) and Ar^(*4), equal to or         different from each other at each occurrence, is an aromatic         moiety:     -   n* and m*, equal to or different from each other, are         independently zero or an integer of 1 to 5;     -   T* is a bond or a divalent group optionally comprising one or         more than one heteroatom; preferably T* is selected from the         group consisting of a bond, —CH₂—, —C(CH₃)₂—, —C(CF₃)₂—,         —C(═CCl₂)—, —C(CH₃)(CH₂CH₂COOH)—, and a group of formula:

and

-   -   E is a 1,4:3,6-dianhydrohexitol sugar diol unit selected from         one or more of formulae (E-1) to (E-3):

Preferred aromatic moieties Ar^(*1)-Ar^(*4) have the following structures:

wherein:

-   -   each R* is independently selected from the group consisting of         halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether,         carboxylic acid, ester, amide, imide, alkali or alkaline earth         metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal         phosphonate, alkyl phosphonate, amine and quaternary ammonium;         and     -   j* is zero or an integer of 1 to 4 and j*′ is zero or an integer         of 1 to 3.

Polymers (SP) according to this second preferred embodiment of the invention can be manufactured by reaction of at least one 1,4:3,6-dianhydrohexitol [diol (AA)] as defined above with

-   -   at least one dihaloaryl compound [herein after dihalo (BB)] of         formula (S):

X—Ar^(*1)—SO₂—[Ar^(*2)-(T*-Ar^(*3))_(n*)—SO₂]_(m*)—Ar^(*4)—X′

wherein:

-   -   X and X′, equal to or different from each other, are halogens         selected from F, Cl, Br, I; preferably Cl or F; and     -   Ar^(*1), Ar^(*2), Ar^(*3), Ar^(*4), T*, n* and m* are as defined         above.

A convenient method for manufacturing polymers (SP) according to this second preferred embodiment of the invention is disclosed in WO 2014/072473 (SOLVAY SPECIALTY POLYMERS ITALY S.P.A.) 15 May 2014, incorporated by reference herein.

Non limiting examples of polymers (SP) according to this second preferred embodiment of the invention include poly(isosorbide) polymers [polymers (PSI)].

For the purpose of the present invention, the term “poly(isosorbide) polymer [polymer (PSI)]” is intended to denote any polymer comprising recurring units wherein more than 30% by moles of the recurring units (R_(SP-2)) of said polymer (PSI) are recurring units (R_(PSI)) independently selected from one or more of those of formulae (R_(PSI)-1) and (R_(PSI)-2):

wherein:

-   -   each of R*, equal to or different from each other, is as defined         above;     -   j* is as defined above;     -   T* is as defined above and is preferably selected from the group         consisting of a bond, —CH₂—, —C(O)—, —C(CH₃)₂—, —C(CF₃)₂—,         —C(═CCl₂)—, —C(CH₃)(CH₂CH₂COOH)—, —SO₂—, phenylene and a group         of formula:

and

-   -   E is a 1,4:3,6-dianhydrohexitol sugar diol unit of formulae         (E-1)         [hereinafter also referred to as isosorbide unit (E-1)].

Recurring units (R_(PSI)-1) and (R_(PSI)-2) can be each present alone or in admixture.

More preferred polymers (PSI) are those comprising recurring units of formulae (R_(PSI)-1) and (R_(PSI)-2), wherein E is a 1,4:3,6-dianhydrohexitol sugar diol unit of formula (E-1), optionally in combination with one or more (R_(PSI)-1) and (R_(PSI)-2) units, wherein E is a 1,4:3,6-dianhydrohexitol sugar diol unit of formula (E-2) and/or (E-3) [hereinafter also referred to as isomannide and isoidide units (E-2) and (E-3), respectively].

Most preferred polymers (PSI) are those comprising recurring units of formula (R_(PSI)-1), wherein E is an isosorbide unit (E-1), optionally in combination with recurring units (R_(PSI)-1), wherein E is an isomannide unit of formula (E-2) and/or an isoidide unit of formula (E-3).

In recurring units (R_(PSI)-1) and (R_(PSI)-2), the respective phenylene moieties may independently have 1,2-, 1,4- or 1,3-linkages to the other moieties different from R* in the recurring units. Preferably, said phenylene moieties have 1,3- or 1,4-linkages, more preferably they have 1,4-linkages. Still, in recurring units (R_(PSI)-1) and (R_(PSI)-2), j* is at each occurrence zero, that is to say that the phenylene moieties have no other substituents than those enabling linkage in the main chain of the polymer.

Polymers (PSI) may optionally further comprise recurring units selected from one or more of:

-   -   recurring units (R_(A′A′)), deriving from the incorporation of         at least one dihydroxyl compound [diol (A′A′)] different from         diol (AA);     -   recurring units (R_(B′B′)), deriving from the incorporation of         at least one dihaloaryl compound [dihalo (B′B′)] different from         dihalo (BB);     -   recurring units (R_(A′B′)), deriving from the incorporation of         at least one hydroxyl-halo compound [hydro-halo (A′B′)];     -   recurring units (R_(c)) of formula (S1):

Ar⁵-(T^(S1)-Ar⁶)_(q)—O—Ar⁷—SO₂—[Ar₈-(T^(S1′)-Ar⁹)_(q)—SO₂]_(p)—Ar¹⁰—O—

wherein:

-   -   Ar⁵, Ar⁶, Ar⁷, Ar⁸ and Ar⁹, equal to or different from each         other and at each occurrence, are independently an aromatic         moiety;     -   T^(S1) and T^(S1′), equal to or different from each other at         each occurrence, are independently a bond or a divalent group         optionally comprising one or more than one heteroatom;         preferably T^(S1) and T^(S1′) are selected from the group         consisting of a bond, —CH₂—, —C(O)—, —C(CH₃)₂—, —C(CF₃)₂—,         —C(═CCl₂)—, —C(CH₃)(CH₂CH₂COOH)—, —SO₂—, and a group of formula:

-   -   q and p, equal to or different from each other, are         independently zero or an integer of 1 to 5.

Recurring units (R_(c)) can be notably selected from the group consisting of those of formulae (S1-A) to (S1-D) here below:

wherein:

-   -   each of R^(c′), equal to or different from each other, is         selected from the group consisting of halogen, alkyl, alkenyl,         alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide,         imide, alkali or alkaline earth metal sulfonate, alkyl         sulfonate, alkali or alkaline earth metal phosphonate, alkyl         phosphonate, amine and quaternary ammonium;     -   j^(c′) is zero or is an integer from 0 to 4;     -   T_(S1) and T_(S1′) are as defined above.

In recurring units of any of formulae (S1-C) to (S1-D), the respective phenylene moieties may independently have 1,2-, 1,4- or 1,3-linkages to the other moieties different from R′ in the recurring unit. Preferably, said phenylene moieties have 1,3- or 1,4-linkages, more preferably they have 1,4-linkages. Still, in recurring units of any of formulae (S1-C) to (S1-D), j^(c′) is at each occurrence zero, that is to say that the phenylene moieties have no other substituents than those enabling linkage in the main chain of the polymer.

Polymers (PSI) typically comprise recurring units of formula (R_(PSI)) as defined above in an amount of at least 30% by moles, preferably 35% by moles, more preferably 40% by moles, even more preferably at least 50% by moles, with respect to all recurring units of polymers (PSI).

According to certain preferred embodiments, more than 70% by moles, and more preferably more than 85% by moles of the recurring units of the polymers (PSI) are recurring units (R_(PSI)), as defined above, the complement to 100% moles being generally recurring units (R_(c)) as defined above.

Methods for the manufacture of polymers (PSI) further comprising recurring units in addition to units (R_(PSI)) are also disclosed in the aforementioned WO 2014/072473 (SOLVAY SPECIALTY POLYMERS ITALY S.P.A.) May 15, 2014.

Preferably, the polymers (PSI) consist only of recurring units (R_(PSI)) as defined above, preferably recurring units (R_(PSI)-1), wherein (E) is an isosorbide unit of formula (E-1) and wherein the phenylene units have 1,4-linkages.

The polymers (PSI) have in general a weight average molecular weight of at least 20,000, preferably at least 30,000, more preferably at least 40,000. The weight average molecular weight (M_(w)) and the number average molecular weight (M_(n)) can be estimated by gel-permeation chromatography (GPC) using ASTM D5296 calibrated with polystyrene standards.

The weight average molecular weight (M_(w)) is:

$M_{w} = \frac{\sum{M_{i}^{2} \cdot N_{i}}}{\sum{M_{i} \cdot N_{i}}}$

The number average molecular weight (M_(n)) is:

$M_{n} = \frac{\sum{M_{i} \cdot N_{i}}}{\sum N_{i}}$

The polydispersity index (PDI) is hereby expressed as the ratio of weight average molecular weight (M_(w)) to number average molecular weight (M_(n)).

Polymers (PSI) generally have a polydispersity index of less than 2.5, preferably of less than 2.4, more preferably of less than 2.2. This relatively narrow molecular weight distribution is representative of an ensemble of molecular chains with similar molecular weights and substantially free from oligomeric fractions, which might have a detrimental effect on polymer properties.

Polymers (PSI) advantageously possess a glass transition temperature of at least 200° C., preferably 210° C., more preferably at least 220° C. Glass transition temperature (Tg) is generally determined by differential scanning calorimetry (DSC) according to ASTM D 3418 standard procedure.

Polymer (PP) preferably comprises at least about 10 mole percent (per 100 moles of polymer (PP)), more preferably at least 12 mole percent and even more preferably at least 15 mole percent, of repeat units (R_(pm)) represented by the following formula

and at least about 10 mol percent repeat units (R_(pp)) represented by the following formula:

wherein R¹, R², R³, R⁴ R⁵, R⁶, R⁷, and R⁸ are each independently selected from the group consisting of hydrogen, alkyl, aryl, alkoxy, aryloxy, alkylketone, arylketone, fluoroalkyl, fluoroaryl, bromoalkyl, bromoaryl, chloroalkyl, chloroaryl, alkylsulfone, arylsulfone, alkylamide, arylamide, alkylester, arylester, fluorine, chlorine, and bromine.

Preferably, one or more of R¹, R², R³, and R⁴ is independently represented by formula Ar-T-,

wherein Ar is represented by a formula selected from the following group of formulae:

wherein each R_(j), R_(k) and R_(l) is independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium, with j and l, equal or different from each other, being independently 0, 1, 2, 3, 4, or 5 and, k, equal or different from j or l, being independently 0, 1, 2, 3 or 4; T is selected from the group consisting of —CH₂—; —O—; —SO₂—; —S—; —C(O)—; —C(CH₃)₂—; —C(CF₃)₂—; —C(═CCl₂)—; —C(CH₃)(CH₂CH₂COOH)—; —N═N—; —R^(a)C═CR^(b)—, wherein each R^(a) and R^(b), independently of one another, is hydrogen, C₁-C₁₂-alkyl, C₁-C₁₂-alkoxy, or C₆-C₁₈-aryl group; —(CH₂)_(n)— and —(CF₂)_(n)— with n being an integer from 1 to 6; a linear or branched aliphatic divalent group having from 1 to 6 carbon atoms.

In some embodiments, one or more of R¹, R², R³, and R⁴ is represented by formula:

In some embodiments, the repeat unit (R_(pm)) is represented by the formula

In some embodiments, the polymer (PP) comprises at least about 30 mole percent, preferably at least about 40 mole percent of repeating units (R_(pm)).

In some embodiments, one or more of R⁵, R⁶, R⁷, and R⁸ is independently represented by formula Ar″-T″-,

wherein Ar″ is represented by a formula selected from the following group of formulae

wherein each R_(j″), R_(k″) and R_(l′) is independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium, j″ and l″, equal or different from each other being independently 0, 1, 2, 3, 4, or 5 and, k″, equal or different from j″ or l″, being independently 0, 1, 2, 3 or 4; T″ is selected from the group consisting of —CH₂—; —O—; —SO₂—; —S—; —C(O)—; —C(CH₃)₂—; —C(CF₃)₂—; —C(═CCl₂)—; —C(CH₃)(CH₂CH₂COOH)—; —N═N—; —R^(a)C═CR^(b)—, wherein each R^(a) and R^(b), independently of one another, is hydrogen, C₁-C₁₂-alkyl, C₁-C₁₂-alkoxy, or C₆-C₁₈-aryl group; —(CH₂)_(n)— and —(CF₂)_(n)— with n being an integer from 1 to 6; a linear or branched aliphatic divalent group having from 1 to 6 carbon atoms.

In some embodiments, the repeat unit (R_(pp)) is represented by the formula:

In some embodiments, the polymer (PP) comprises at least about 40 mole percent repeat units (R_(pp)).

In a preferred embodiment, said polymer (PP) is commercially available from Solvay Specialty Polymers, under the tradename PrimoSpire® SRP.

Said medium (L) is advantageously selected from polar aprotic solvents.

The medium (L) preferably comprises at least one organic solvent.

Suitable examples of organic solvents are:

-   -   aliphatic hydrocarbons including, more particularly, the         paraffins such as, in particular, pentane, hexane, heptane,         octane, nonane, decane, undecane, dodecane or cyclohexane, and         naphthalene and aromatic hydrocarbons and more particularly         aromatic hydrocarbons such as, in particular, benzene, toluene,         xylenes, cumene, petroleum fractions composed of a mixture of         alkylbenzenes;     -   aliphatic or aromatic halogenated hydrocarbons including more         particularly, perchlorinated hydrocarbons such as, in         particular, tetrachloroethylene, hexachloroethane;     -   partially chlorinated hydrocarbons such as dichloromethane,         chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane,         1,1,2,2-tetrachloroethane, pentachloroethane, trichloroethylene,         1-chlorobutane, 1,2-dichlorobutane, monochlorobenzene,         1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene,         1,2,4-trichlorobenzene or mixture of different chlorobenzenes;     -   aliphatic, cycloaliphatic or aromatic ether oxides, more         particularly, diethyl oxide, dipropyl oxide, diisopropyl oxide,         dibutyl oxide, methylterbutyl ether, dipentyl oxide, diisopentyl         oxide, ethylene glycol dimethyl ether, ethylene glycol diethyl         ether, ethylene glycol dibutyl ether benzyl oxide; dioxane,         tetrahydrofuran (THF);     -   dimethylsulfoxide (DMSO);     -   glycol ethers such as ethylene glycol monomethyl ether, ethylene         glycol monoethyl ether, ethylene glycol monopropyl ether,         ethylene glycol monoisopropyl ether, ethylene glycol monobutyl         ether, ethylene glycol monophenyl ether, ethylene glycol         monobenzyl ether, diethylene glycol monomethyl ether, diethylene         glycol monoethyl ether, diethylene glycol mono-n-butyl ether;     -   glycol ether esters such as ethylene glycol methyl ether         acetate, ethylene glycol monoethyl ether acetate, ethylene         glycol monobutyl ether acetate;     -   alcohols, including polyhydric alcohols, such as methyl alcohol,         ethyl alcohol, diacetone alcohol, ethylene glycol;     -   ketones such as acetone, methylethylketone, methylisobutyl         ketone, diisobutylketone, cyclohexanone, isophorone;     -   linear or cyclic esters such as isopropyl acetate, n-butyl         acetate, methyl acetoacetate, dimethyl phthalate,         γ-butyrolactone;     -   linear or cyclic carboxamides such as N,N-dimethylacetamide         (DMAc), N,N-diethylacetamide, dimethylformamide (DMF),         diethylformamide or N— methyl-2-pyrrolidone (NMP);     -   organic carbonates for example dimethyl carbonate, diethyl         carbonate, dipropyl carbonate, dibutyl carbonate, ethylmethyl         carbonate, ethylene carbonate, vinylene carbonate;     -   phosphoric esters such as trimethyl phosphate, triethyl         phosphate (TEP);     -   ureas such as tetramethylurea, tetraethylurea;     -   methyl-5-dimethylamino-2-methyl-5-oxopentanoate (commercially         available under the tradename Rhodialsov Polarclean®).

Preferably, said at least one organic solvent is selected from polar aprotic solvents and even more preferably in the group consisting of: N-methyl-pyrrolidone (NMP), dimethyl acetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), methyl-5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the tradename Rhodialsov Polarclean®) and triethylphosphate (TEP).

The medium (L) preferably comprises at least 40 wt. %, more preferably at least 50 wt. % based on the total weight of said medium (L), of at least one organic solvent. Medium (L) preferably comprises at most 100 wt. %, more preferably at most 99 wt. % based on the total weight of said medium (L), of at least one organic solvent.

The medium (L) may further comprise at least one non-solvent medium [medium (NS)]. The medium (NS) may comprise water.

Preferably, said fluid containing at least one contaminant is a liquid phase or a gas phase.

Said contaminant can be a solid contaminant. According to this embodiment, liquid and gas phases comprising one or more solid contaminants are also referred to as “suspensions”, i.e. heterogeneous mixtures comprising at least one solid particle (the contaminant) dispersed into a continuous phase (or “dispersion medium”, which is in the form of liquid or gas).

Said at least one solid contaminant preferably comprises comprising microorganisms, preferably selected from the group consisting of bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa, algae, fungi, protozoa and viruses.

According to another embodiment, when saline water is the liquid phase, said contaminant is the dissolved salt content in the saline water itself. According to this embodiment, the liquid phase is an “aqueous solution”, i.e. a homogeneous mixture wherein salts (the solute) are dissolved into water (the solvent).

In a preferred embodiment, the method of the present invention is a method for purifying non-drinkable water, wherein said fluid is saline water or brackish water, said contaminant is the dissolved salts content, and said membrane (PSP) comprises (I) a substrate layer, (II) an outer layer consisting of aromatic polyamides and (III) a layer (PSP) as defined above, said layer (PSP) being interposed between said substrate layer and said outer layer.

In one embodiment, two or more membranes (PSP) can be used in series for the filtration of a liquid and/or gas phase. Advantageously, a first filtration step is performed by contacting liquid and/or gas phases comprising one or more solid contaminants with a first membrane [membrane (PSP1)] having an average pore diameter higher than 5 μm, more preferably from 5 to 50 μm; and a second filtration step is performed after said first filtration step, by contacting the same liquid and/or gas phase with a second membrane [membrane (PSP2)] having an average pore diameter of from 0.001 to 5 μm.

Alternatively, at least one membrane (PSP) is used in series with at least one porous membrane obtained from a composition different composition (C) according to the present invention.

Preferably, said step (iii) is performed by applying a pressure of at least 2 bar, preferably of at least 4 bars. Preferably, said step (iii) is performed by applying a pressure up to 50 bar, more preferably up to 100 bar.

Membrane (PSP) can be manufactured according to techniques known in the art, for example in liquid phase or in molten phase.

According to a first embodiment of the invention, the process for manufacturing a porous membrane is carried out in liquid phase.

The process according to this first embodiment preferably comprises:

(i{circumflex over ( )}) providing a liquid composition [composition (C^(L))] comprising:

-   -   polymer (SP) as defined above,     -   polymer (PP) as defined above, and     -   medium (L) as defined above;

(ii{circumflex over ( )}) processing composition (C^(L)) provided in step (i) thereby providing a film; and

(iii{circumflex over ( )}) precipitating the film provided in step (ii) thereby providing a porous membrane.

Under step (i{circumflex over ( )}), composition (C^(L)) is manufactured by any conventional techniques. For instance, the medium (L) may be added to one of polymer (SP) and polymer (PP) and then the remaining polymer is added, or, preferably, polymer (SP) or polymer (PP) may be added to the medium (L) and then the remaining polymer is added, or even polymer (PP), polymer (SP) and the medium (L) may be simultaneously mixed.

Any suitable mixing equipment may be used. Preferably, the mixing equipment is selected to reduce the amount of air entrapped in composition (C^(L)) which may cause defects in the final membrane. The mixing of the each of polymer (PP) and polymer (SP) and the medium (L) may be conveniently carried out in a sealed container, optionally held under an inert atmosphere. Inert atmosphere, and more precisely nitrogen atmosphere has been found particularly advantageous for the manufacture of composition (C^(L)).

Under step (i{circumflex over ( )}), the mixing time during stirring required to obtain a clear homogeneous composition (C^(L)) can vary widely depending upon the rate of dissolution of the components, the temperature, the efficiency of the mixing apparatus, the viscosity of composition (C^(L)) and the like.

Under step (ii{circumflex over ( )}), composition (C^(L)) is typically processed in liquid phase.

Under step (ii{circumflex over ( )}), composition (C^(L)) is typically processed by casting thereby providing a film.

Casting generally involves solution casting, wherein typically a casting knife, a draw-down bar or a slot die is used to spread an even film of a liquid composition comprising a suitable medium (L) across a suitable support.

Under step (ii{circumflex over ( )}), the temperature at which composition (C^(L)) is processed by casting may be or may be not the same as the temperature at which composition (C^(L)) is mixed under stirring.

Different casting techniques are used depending on the final form of the membrane to be manufactured.

When the final product is a flat membrane, composition (C^(L)) is cast as a film over a flat supporting substrate, typically a plate, a belt or a fabric, or another microporous supporting membrane, typically by means of a casting knife, a draw-down bar or a slot die.

According to a first embodiment of step (ii{circumflex over ( )}), composition (C^(L)) is processed by casting onto a flat supporting substrate to provide a flat film.

According to a second embodiment of step (ii{circumflex over ( )}), composition (C^(L)) is processed to provide a tubular film.

According to a variant of this second embodiment of step (ii{circumflex over ( )}), the tubular film is manufactured using a spinneret.

The term “spinneret” is hereby understood to mean an annular nozzle comprising at least two concentric capillaries: a first outer capillary for the passage of composition (C^(L)) and a second inner one for the passage of a supporting fluid, generally referred to as “lumen”.

Hollow fibers and capillary membranes may be manufactured by the so-called spinning process according to this variant of the second embodiment of step (ii{circumflex over ( )}). According to this variant of the second embodiment of the invention, composition (C^(L)) is generally pumped through the spinneret. The lumen acts as the support for the casting of composition (C^(L)) and maintains the bore of the hollow fiber or capillary precursor open. The lumen may be a gas, or, preferably, a medium (NS) or a mixture of the medium (NS) with a medium (L). The selection of the lumen and its temperature depends on the required characteristics of the final membrane as they may have a significant effect on the size and distribution of the pores in the membrane.

At the exit of the spinneret, after a short residence time in air or in a controlled atmosphere, under step (iii{circumflex over ( )}) of the process for manufacturing a porous membrane according to this first embodiment of the invention, the hollow fiber or capillary precursor is precipitated thereby providing the hollow fiber or capillary membrane.

The supporting fluid forms the bore of the final hollow fiber or capillary membrane.

Tubular membranes, because of their larger diameter, are generally manufactured using a different process from the one employed for the production of hollow fiber membranes.

The Applicant has found that use of solvent/non-solvent mixtures at a given temperature, in any one of steps (ii{circumflex over ( )}) and (iii{circumflex over ( )}) of the process according to the invention, advantageously allows controlling the morphology of the final porous membrane including its average porosity.

The temperature gradient between the film provided in any one of steps (ii{circumflex over ( )}) and (iii{circumflex over ( )}) of the process according to the first embodiment of the invention and the medium (NS) may also influence the pore size and/or pore distribution in the final porous membrane as it generally affects the rate of precipitation of the polymer (A) from composition (C^(L)).

According to a second embodiment of the invention, the process for manufacturing a porous membrane is carried out in molten phase.

The process according to the second embodiment of the invention preferably comprises the following steps: (i{circumflex over ( )}{circumflex over ( )}) providing a solid composition [composition (C^(S))] comprising at least one polymer (PP) and polymer (SP) as defined above; (ii{circumflex over ( )}{circumflex over ( )}-A) processing the composition (C^(S)) provided in step (i{circumflex over ( )}{circumflex over ( )}) thereby providing a film and (iii{circumflex over ( )}{circumflex over ( )}-A) stretching the film provided in step (ii{circumflex over ( )}{circumflex over ( )}-A) thereby providing a porous membrane; or (ii{circumflex over ( )}{circumflex over ( )}-B) processing the composition (C^(S)) provided in step (i{circumflex over ( )}{circumflex over ( )}) thereby providing fibers and (iii{circumflex over ( )}{circumflex over ( )}-B) processing the fibers provided in (ii{circumflex over ( )}{circumflex over ( )}-B) thereby providing a porous membrane.

Under step (ii{circumflex over ( )}{circumflex over ( )}-A), composition (C^(S)) is preferably processed in molten phase.

Melt forming is commonly used to make dense films by film extrusion, preferably by flat cast film extrusion or by blown film extrusion.

According to this technique, composition (C^(S)) is extruded through a die so as to obtain a molten tape, which is then calibrated and stretched in the two directions until obtaining the required thickness and wideness. Composition (C^(S)) is melt compounded for obtaining a molten composition. Generally, melt compounding is carried out in an extruder. Composition (C^(S)) is typically extruded through a die at temperatures of generally lower than 250° C., preferably lower than 200° C. thereby providing strands which are typically cut thereby providing pellets.

Twin screw extruders are preferred devices for accomplishing melt compounding of composition (C^(S)).

Films can then be manufactured by processing the pellets so obtained through traditional film extrusion techniques. Film extrusion is preferably accomplished through a flat cast film extrusion process or a hot blown film extrusion process. Film extrusion is more preferably accomplished by a hot blown film extrusion process.

Under step (iii{circumflex over ( )}{circumflex over ( )}-A), the film provided in step (ii{circumflex over ( )}{circumflex over ( )}-A) may be stretched either in molten phase or after its solidification upon cooling.

The porous membrane obtainable by the process of the invention is typically dried, preferably at a temperature of at least 30° C.

Drying can be performed under air or a modified atmosphere, e.g. under an inert gas, typically exempt from moisture (water vapour content of less than 0.001% v/v). Drying can alternatively be performed under vacuum.

As used within the present description, “composition (C)” is intended to include both the liquid composition [composition (C^(L))] and the solid composition [composition (C^(S))], unless otherwise specified.

According to a preferred embodiment, composition (C) is free of plasticizer agents, i.e. plasticizer agents are not added to composition (C) or they are present in an amount of less than 1 wt. %, more preferably less than 0.1 wt. % based on the total weight of said composition (C).

Preferably, said composition (C^(L)) comprises said polymer (PP) in an amount of from 0.1 to less than 30 wt. % based on the total weight of said composition (C^(L)) and said polymer (SP) in an amount of from 7 to 60 wt. % based on the total weight of said composition (C^(L)), the remaining amount up to 100 wt. % of said composition (C^(L)) being provided by medium (L) as defined above.

Preferably, said composition (C^(L)) comprises said polymer (PP) in an amount of from 0.5 to 29 wt. %, more preferably from 0.9 to 20 wt. % based on the total weight of said composition (C^(L)).

Preferably, said composition (C^(L)) comprises said polymer (SP) in an amount of from 8 to 55 wt. %, more preferably from 10 to 50 wt. % based on the total weight of said composition (C^(L)).

Preferably, said composition (C^(S)) comprises said polymer (PP) in an amount of from 0.1 to 50 wt. % based on the total weight of said composition (C^(S)) and said polymer (SP) in an amount of from 50 to 99.9 wt. % based on the total weight of said composition (C^(S)).

A preferred embodiment of membrane (PSP) according to the present invention is the embodiment referred to as membrane (PSP*).

Preferably, composition (C*) has the features described above for composition (C^(L)).

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

The invention will be herein after illustrated in greater detail by means of the Examples contained in the following Experimental Section; the Examples are merely illustrative and are by no means to be interpreted as limiting the scope of the invention.

EXPERIMENTAL SECTION

Raw Materials

Dimethylacetamide (DMAC), N-Methyl pirrolidone (NMP), isopropyl alcohol (IPA) and PolyVinyl Pirrolidone (PVP) K10 were obtained from Sigma Aldrich.

Veradel® 3000P (polyethersulfone—PESU), Udel® P-3500 LCD (polysulfone—PSU), Radel® R 5000 NT (PPSU) and Primospire® PR 250 (polyphenylene) were obtained from Solvay Specialty Polymers.

Methods

Mechanical (Tensile) Test on Flat Sheet Membranes

Mechanical properties on flat sheet porous membranes were assessed at room temperature (23° C.) following ASTM norm D638 type V, with a Grip distance=25.4 mm, and initial length L₀=21.5 mm. Velocity was between 1 and 50 mm/min.

The samples stored in water were took out from the container boxes and immediately tested to determine apparent modulus and stress at break.

Mechanical (Tensile) Test on Hollow Fiber Membranes

All the tests on the extruded fibers were performed following the ASTM D3032 method with an initial length L₀=125 mm and velocity of 125 mm/min.

All the tested fibers were stored in water without any supplementary treatment. During the tests the fibers were maintained wet: each test involved at least four-five iterations on several fiber specimens. Apparent modulus and stress at break were determined.

Measurement of Porosity and Pore Sizes

Gravimetric porosity of the membrane is defined as the volume of the pores divided by the total volume of the membrane. The porosities were measured using IPA (isopropyl alcohol) as wetting fluid according to the procedure described in Appendix of Desalination, 72 (1989) 249-262.

$ɛ = \frac{\frac{\left( {{Wet} - {Dry}} \right)}{\rho_{liquid}}}{\frac{\left( {{Wet} - {Dry}} \right)}{\rho_{liquid}} - \frac{Dry}{\rho_{polymer}}}$

where Wet is the weight of the wetted membrane, Dry is the weight of dry membrane, ρ_(polymer) is the density of the polymer (PrimoSpire® 1.19 g/cm³; 1.36 g/cm³ PESU; 1.24 g/cm³ PSU; 1.29 g/cm³ PPSU) and ρ_(liquid) is the density of IPA (0.78 g/cm³).

Measurement of Water Permeability

The pure water permeability was measured according to the technique known in the art. Water flux (J) through each membrane at given pressure, was defined as the volume which permeates per unit area and per unit time. The flux is calculated by the following equation:

$J = \frac{V}{A\;\Delta\; t}$

where V (L) is the volume of permeate, A is the membrane area, and Δt is the operation time.

Water flux measurements on flat sheet membranes were conducted at room temperature using a dead-end configuration under a constant nitrogen.

Flux Decay Tests (“Compaction Tests”)

This test was performed to assess the propensity of the produced items to pressure compaction. This test was performed only on some selected flat sheet items and consists in measuring the flux (as defined above) for prolonged times (about 45 minutes) for each of three pre-determined consecutive steps at 1-2 and 4 bar of applied pressure. The first flux measurement at 1 bar was performed after roughly 11 minutes of holding the pressure. The entire test lasted for 135 minutes. At the end, it was possible to assess the flux decay during the duration of each pressure step and also check the eventual proportionality between flux and applied pressure.

Preparation of Dope Solutions

Solutions were prepared at 30° C., by adding the amount of polymer detailed in the examples that follows and optional additives in the solvent (DMAC or NMP as detailed below) and stirring with a mechanical anchor for several hours until a clear and homogeneous system for each solution was obtained. When necessary, the temperature of the system was raised to 50° C.-60° C. in order to speed up the dissolution process.

Preparation of Membranes in the Form of Flat Sheet

Porous membranes in the form of flat sheets were prepared by filming the dope solution prepared as described above over a suitable smooth glass support, by means of an automatized casting knife.

Membrane casting was performed by holding the dope solution, the casting knife and the support temperatures at 25° C., so as to prevent premature precipitation of the polymer. The knife gap was set at 250 μm. After casting, polymeric films were immediately immersed in a coagulation bath (either of pure de-ionized water or a mixture IPA/water 50:50 v/v) in order to induce phase inversion.

After coagulation the membranes were washed several times in pure water in the following days to remove residual traces of solvent.

Preparation of Membranes in the Form of Hollow Fibers

Porous membranes in the form of hollow fibers were prepared by extruding the dope solution, prepared as detailed above, through a spinneret.

Hollow fibers were prevented from collapsing by coextruding water as bore fluid in the center of the annulus, which was fed at a flow rate ranging from 1-10 ml/min.

The rotating (coagulation) water bath enabled producing coagulation by phase inversion. The temperature of the apparatus was controlled by a PID system. The spinneret geometry used in the extrusion part had an internal diameter (IDsp) of 800 μm, an external one of 1600 μm (ODsp) and a bore diameter of 300 μm (indicated later in the text as 0.3-0.8-1.6).

Example 1

Porous membranes according to the invention in the form of flat sheets were prepared using DMAC solvent and the following blends:

(a) Radel® PPSU 18% w/w+Primospire® PR-2502% w/w (b) Radel® PPSU 18% w/w+Primospire® PR-2504% w/w

The nascent membranes were coagulated in water.

Example 1C(*)

As comparison, porous membranes in the form of flat sheets were prepared using DMAC solvent and Radel® PPSU 20% w/w.

The nascent membrane was coagulated in water.

The mechanical properties for the membranes obtained are shown in the following Table 1.

TABLE 1 Example 1 (a) (b) Example 1C(*) Modulus (MPa) 266 283 233 Stress at break 11.3 11.9 11.1 (MPa) Porosity 0.781 0.778 0.760 (*)comparison

The above results showed that an improvement of about 14% in the tensile modulus of the membrane prepared according to Example 1 method (a) was obtained already when using only 2 wt. % of Primospire® as additive.

Example 2

Porous membranes according to the invention in the form of flat sheets were prepared using DMAC solvent and a blend comprising 5% w/w of PVP K10, 10% w/w Primospire® PR-250 and 10% w/w of Radel® PPSU.

The nascent membrane was coagulated in water.

Example 2C(*)

As comparison, porous membranes in the form of flat sheets were prepared using DMAC solvent and a blend comprising 5% w/w of PVP K10 and 20% w/w of Radel® PPSU.

The nascent membrane was coagulated in water.

Compaction test was performed on the membranes prepared as described above. The results are shown in the following Table 2.

TABLE 2 Example 2 Example 2C(*) Applied Time Flux/(initial Flux/(initial pressure (bar) (min) flux at 1 bar) flux at 1 bar) 1 11 1.00 1.00 1 21 0.97 0.93 1 31 0.95 0.88 1 41 0.94 0.83 2 56 1.65 1.24 2 66 1.62 1.15 2 76 1.58 1.09 2 86 1.56 1.03 4 101 2.60 1.34 4 111 2.48 1.25 4 121 2.39 1.16 4 131 2.30 1.10 (*)comparison

The above results showed that the membrane prepared according to the invention retained a better flux at each pressure step and notably at 2 bar and above, and that, as pressure increased, a proportionality between flux and pressure was maintained. On the contrary, as pressure increased, the flux measured for the comparative membrane was strongly affected by pressure compaction.

Example 3

Porous membranes according to the invention in the form of hollow fibers were prepared using NMP as solvent and a blend of 14% w/w of Veradel® PES 3000 MP+4% w/w Primospire®.

Example 3C(*)

As comparison, porous membranes in the form of hollow fibers were prepared using NPM as solvent and 18% w/w Veradel® PESU 3000 MP (polyethersulfone).

The experimental conditions for the preparation of the membranes of Example 3 and Example 3C were the following:

-   -   dope composition/T° C. extrusion: 18 wt. %/30° C.     -   nozzle (mm): 0.3-0.8-1.6     -   bore fluid: pure water     -   coagulation bath temperature: water at 25° C.     -   ratio of Dope throughput (g/min) to Bore throughput (D/B ratio):         0.4-1.1     -   air gap: 9 cm

The mechanical properties for the membranes obtained are shown in the following Table 3.

TABLE 3 Example 3 Example 3C(*) Modulus (MPa) 158 115 Stress at break (MPa) 7.0 5.4 Porosity 0.802 0.825 (*) comparison

The results in Table 3 showed that remarkable improvement in the mechanical properties of the membranes prepared according to the invention was obtained when using Primospire® PR-250 polymer as additive.

Examples 4C(*)

Porous membrane (Example 4C*) in the form of flat sheet was prepared using DMAC solvent, Udel® PSU P-3500LCD 5% w/w and PrimoSpire® PR250 5% w/w.

The membrane was coagulated in water.

The membrane of Example 4C showed no mechanical integrity upon handling and hence it was not possible to measure its mechanical properties.

Example 5C(*)

A composition (Example 5C*) comprising DMAC solvent, Udel® PSU P-3500LCD 30% w/w and PrimoSpire® PR25030% w/w was prepared.

From the composition, it was not possible to cast film a membrane. Indeed, either using a magnetic or a mechanical stirrer and heating up to 130° C., it was not possible to dissolve the PrimoSpire® PR250 polymer. 

1-15. (canceled)
 16. A method for purifying a fluid containing at least one contaminant, said method comprising the steps of (I) providing a fluid containing at least one contaminant; (II) providing a membrane [membrane (PSP)] comprising at least one porous layer [layer (PSP)] comprising at least one aromatic sulfone polymer [polymer (SP)] and at least one polyphenylene polymer [polymer (PP)]; (III) contacting said fluid containing at least one contaminant and said membrane (PSP) by applying a pressure higher than 1 bar to said fluid; and (IV) recovering the fluid free from said at least one contaminant.
 17. The method according to claim 1, wherein said membrane (PSP) comprises said layer (PSP) as the only layer or said membrane (PSP) is a multi-layered membrane.
 18. The method according to claim 1, wherein said polymer (SP) is a polymer comprising at least one group of formula —Ar—SO₂—Ar′— [recurring units (R_(SP))], wherein Ar and Ar′, equal to or different from each other, are aromatic groups, and wherein more than 50% by moles of the recurring units of said polymer (SP) are connected by ether linkages in the main chain.
 19. The method according to claim 18, wherein the recurring units (R_(SP)) are selected from the group consisting of: (I) recurring units (R_(SP-1)) of formula: —Ar¹-(T′—Ar²)_(n)—O—Ar³—SO₂—[Ar⁴-(T-Ar²)_(n)—SO₂]_(m)—Ar⁵—O—  (R_(SP-1)) wherein: Ar¹, Ar², Ar³, Ar⁴, and Ar⁵, equal to or different from each other and at each occurrence, are independently aromatic mono- or polynuclear groups; T and T′, equal to or different from each other and at each occurrence, is independently a bond or a divalent group optionally comprising one or more than one heteroatoms; preferably T′ is selected from the group consisting of a bond, —CH₂—, —C(O)—, —C(CH₃)₂—, —C(CF₃)₂—, —C(═CCl₂)—, —SO₂—, —C(CH₃)(CH₂CH₂COOH)—, and a group of formula:

and preferably T is selected from the group consisting of a bond, —CH₂—, —C(O)—, —C(CH₃)₂—, —C(CF₃)₂—, —C(═CCl₂)—, —C(CH₃)(CH₂CH₂COOH)—, and a group of formula:

and and m, equal to or different from each other, are independently zero or an integer of 1 to 5; (II) recurring units (R_(SP-2)) of formula: —Ar^(*1)—SO₂—[Ar^(*2)-(T*-Ar^(*3))_(n*)—SO₂]_(m*)—Ar^(*4)-E-  (R_(SP-2)) wherein each of Ar^(*1), Ar^(*2), Ar^(*3) and Ar^(*4), equal to or different from each other at each occurrence, is an aromatic moiety; n* and m*, equal to or different from each other, are independently zero or an integer of 1 to 5; T* is a bond or a divalent group optionally comprising one or more than one heteroatom; preferably T* is selected from the group consisting of a bond, —CH₂—, —C(CH₃)₂—, —C(CF₃)₂—, —C(═CCl₂)—, —C(CH₃)(CH₂CH₂COOH)—, and a group of formula:

and E is a 1,4:3,6-dianhydrohexitol sugar diol unit selected from one or more of formulae (E-1) to (E-3):


20. The method according to claim 18, wherein said polymer (SP) is selected from poly(phenylene sulfone) polymers [polymers (PPSU)], poly(sulfone) polymers [polymers (PSU)] and poly(ether sulfone) polymers [polymers (PESU)].
 21. The method according to claim 20, wherein said poly(phenylene sulfone) polymer [polymer (PPSU)] is a polymer comprising recurring units wherein more than 50% by moles of the recurring units (R_(SP-1)) of said polymer (PPSU) are recurring units (R_(PPSU)) of formula (K-A):

said poly(sulfone) polymer [polymer (PSU)] is an aromatic sulfone polymer wherein at least 50% by moles of the recurring units (R_(SP-1)) of said polymer (PSU) are recurring units (R_(PSU)) of formula:

said poly(ether sulfone) polymer [polymer (PESU)] is a polymer wherein more than 50% by moles of the recurring units (R_(SP-1)) of said polymer (PESU) are recurring units (R_(PESU)) of formula:

wherein each of R′, equal to or different from each other, is selected from the group consisting of halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium, and each of j′, equal to or different from each other and at each occurrence, is independently zero or is an integer from 0 to
 4. 22. The method according to claim 16, wherein said polymer (PP) comprises at least about 10 mole percent (per 100 moles of polymer (PP)) of repeat units (R_(pm)) represented by the following formula:

and at least about 10 mol percent repeat units (R_(pp)) represented by the following formula

wherein R¹, R², R³, R⁴ R⁵, R⁶, R⁷, and R⁸ are each independently selected from the group consisting of hydrogen, alkyl, aryl, alkoxy, aryloxy, alkylketone, arylketone, fluoroalkyl, fluoroaryl, bromoalkyl, bromoaryl, chloroalkyl, chloroaryl, alkylsulfone, arylsulfone, alkylamide, arylamide, alkylester, arylester, fluorine, chlorine, and bromine.
 23. The method according to claim 22, wherein one or more of R¹, R², R³, and R⁴ is independently represented by formula Ar-T-, wherein Ar is represented by a formula selected from the following group of,

wherein each R_(j), R_(k) and R_(l) is independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium, with j and l, equal or different from each other, being independently 0, 1, 2, 3, 4, or 5 and, k, equal or different from j or l, being independently 0, 1, 2, 3 or 4; T is selected from the group consisting of —CH₂—; —O—; —SO₂—; —S—; —C(O)—; —C(CH₃)₂—; —C(CF₃)₂—; —C(═CCl₂)—; —C(CH₃)(CH₂CH₂COOH)—; —N═N—; —R^(a)C═CR^(b)—, wherein each R^(a) and R^(b), independently of one another, is hydrogen, C₁-C₁₂-alkyl, C₁-C₁₂-alkoxy, or C₆-C₁₈-aryl group; —(CH₂)_(n)— and —(CF₂)_(n)— with n being an integer from 1 to 6; a linear or branched aliphatic divalent group having from 1 to 6 carbon atoms; and/or wherein one or more of R⁵, R⁶, R⁷, and R⁸ is independently represented by formula Ar″-T″-, wherein Ar″ is represented by a formula selected from the following group of formulae

wherein each R_(j″), R_(k″), and R_(l″) is independently selected from the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium, j″ and l″, equal or different from each other being independently 0, 1, 2, 3, 4, or 5 and, k″, equal or different from j″ or l″, being independently 0, 1, 2, 3 or 4; T″ is selected from the group consisting of —CH₂—; —O—; —SO₂—; —S—; —C(O)—; —C(CH₃)₂—; —C(CF₃)₂—; —C(═CCl₂)—; —C(CH₃)(CH₂CH₂COOH)—; —N═N—; —R^(a)C═CR^(b)—, wherein each R^(a) and R^(b), independently of one another, is hydrogen, C₁-C₁₂-alkyl, C₁-C₁₂-alkoxy, or C₆-C₁₈-aryl group; —(CH₂)_(n)— and —(CF₂)_(n)— with n being an integer from 1 to 6; a linear or branched aliphatic divalent group having from 1 to 6 carbon atoms.
 24. The method according to claim 22, wherein the repeat unit (R_(pm)) is represented by the formula

and polymer (PP) comprises at least about 30 mole percent of repeat units (R_(pm)).
 25. The method according to claim 22, wherein the repeat unit (R_(pp)) is represented by the formula

and polymer (PP) comprises at least about 40 mole percent repeat units (R_(pp)).
 26. The method according to claim 1, wherein said method is for purifying non-drinkable water, said fluid is saline water or brackish water, said contaminant is the salts content dissolved into said fluid, and said membrane (PSP) is a multi-layered membrane comprising (I) a substrate layer, (II) an outer layer consisting of aromatic polyamides and (III) the layer (PSP), said layer (PSP) being interposed between said substrate layer and said outer layer.
 27. The method according to claim 1, wherein said fluid containing at least one contaminant is a liquid phase or a gas phase.
 28. The method according to claim 1, wherein said layer (PSP) is obtained from a [composition (C)] comprising at least one polymer (SP), at least one polymer (PP) and at least one solvent [medium (L)].
 29. The method according to claim 28, wherein said composition (C) is a liquid composition [composition (C^(L))] comprising at least one medium (L), at least one polymer (PP) in an amount of from 0.1 to 30 wt. % based on the total weight of said composition (C^(L)) and at least one polymer (SP) in an amount of from 7 to 60 wt. % based on the total weight of said composition (C^(L)), the remaining amount up to 100 wt. % of said composition (C^(L)) being provided by medium (L).
 30. A membrane [membrane (PSP*)] comprising at least one porous layer [layer (PSP*)] obtained from a composition [composition (C*)] comprising at least one sulfone polymer [polymer (SP)] in an amount of from 7 to 60 wt. % based on the total weight of said composition (C*), at least one polyphenylene polymer [polymer (PP)] in an amount of from 0.1 to less than 30 wt. % based on the total weight of said composition (C*), and at least one solvent [medium (L)] in an amount of from 10 to 92.9 wt. % based on the weight of said composition (C*). 